Hi
I set about learning by doing last night
I've read all i can find on this forum with regards chasing.
I found I have about 16mm of plaster on my brick wall.
I used a wide bladed ( ~100mm ) masonary chisel to define the edges and then a smaller 22mm chisel to take out any bits between the edges. I also found that the claw on my hammer (tesco value
) was very good for tidying the inside edges of the channel as it scraped out the plaster easily.
I was quite pleased with the result. The messy edges are more due to the old paint peeling off the existing plaster than anything else.
Eric